In general, a channel measuring apparatus according to the related art is separately embodied with one of a transmitter and a receiver, for transmitting a channel measuring signal or for receiving the transmitted channel measuring signal. Therefore, the channel measuring apparatus according to the related art measures one-directional radio channel.
Since the channel measuring apparatus according to the related art is embodied with one of a transmitter and a receiver, the channel measuring apparatus having the transmitter only transmits a channel measuring signal, and the channel measuring apparatus having the receiver measures a radio channel at a predetermined location by receiving a channel measuring signal.
Therefore, the channel measuring apparatus according to the related art only measures one-directional channel characteristic unlike a bi-directional communication scheme of a mobile communication that wants to use the measured radio channel characteristics.
In a commercial mobile communication network, terminals communication with a base station by transmitting and receiving signals to/from each others. Therefore, it is required to measure not only the characteristics of a downlink channel from a base station to terminals but also the characteristics of an uplink channel from terminals to a base station.
In order to measure the bi-direction channel characteristic using the channel measuring apparatus according to the related art, the downlink characteristics and the uplink characteristics are separately measured. Therefore, it is inconvenient to measure the bi-direction channel characteristics using the channel measuring apparatus according to the related art.
In a time division duplex (TDD) scheme, an uplink and a downlink use the same frequency and have the same channel characteristics. However, the channel characteristics vary according to the channel environment and the location of a terminal, which change with time. Therefore, it is better to measure the downlink channel characteristics and the uplink channel characteristic at the same time. However, it is impossible to measure the characteristics of the uplink and the downlink at the same time.
In a frequency division duplex (FDD) scheme, the uplink and the downlink use different frequencies. Therefore, the channel measuring apparatus according to the related art has a limitation to measure the characteristics of a bi-directional radio channel.
Since the channel measuring apparatus according to the related art uses high cost high power amplifiers as many as the number of multiple antennas, the cost of embodying the channel measuring apparatus according to the related art is high.